The function of the Flow Cytometry and Pathology (Core D) is to provide each Project with the expertise, equipment, and facilities required for the flow cytometric analyses, cell sorting, and pathological analyses that are needed for studies of cardiac mesenchymal cells (CMCs) and extracellular vesicles (EVs). Accurate identification, characterization, and quantitation of cells in a complex heterogeneous population are technically demanding and require specialized and expensive equipment and personnel. One of the major advantages of this Program Project is that it will make available to all four Projects the facilities and techniques of flow cytometry and cell sorting, which otherwise would not be affordable to any Project in isolation. Flow cytometry- based analysis for the identification of specific cell populations, changes in cell commitment or phenotype, and characterization of cell functions such as cell cycle, viability, or signal transduction, will be crucial to all Projects. A central common facility that performs these technically challenging analyses is therefore indispensable to achieve the goals of the Program Project. Besides the obvious advantages of efficiency and cost savings, the Core will also enable four investigators with diverse and complementary backgrounds (Drs. O?Toole, Moore, Li, and Ratajczak) to combine their technical and biological expertise in order to ensure that the proposed work is successfully executed. The Core will offer the Program Project investigators the ability to identify and characterize specific cell types from complex populations. It will also offer the facilities and expertise necessary to perform the comprehensive histopathologic/immunohistochemical analyses required for this Program. The uniform histopathologic analyses conducted by the Core in a blinded and rigorously standardized fashion will make it possible to compare results of different experiments within the same Project and among different Projects. Core D will be the continuation of the Flow Cytometry Core in the current funding cycle (led by Dr. O?Toole) and of the intense and productive ongoing collaboration in flow cytometry and pathology between Dr. O?Toole and the other PPG investigators. The function of Core D is to provide all four Projects with the expertise, equipment, facilities, reagents, procedures, and analyses needed for flow cytometry, sorting, and pathology work. Specifically, the Core will i) perform the flow cytometric analyses and cell sorting procedures required for studies of CMCs and EVs, ii) perform tissue processing, histopathology, and immunohistochemistry of cardiac samples, and iii) make available to the four Projects the tremendous experience and expertise of the Core personnel.